1. Field of the Invention
This invention relates to a contact type line image sensor for use in facsimile machines, document scanners, smart copiers, and the like. Such a line image sensor scans original documents line by line and outputs an electric signal representing the image to a processing circuit.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view of a conventional contact type line image sensor. In this figure, reference numeral 1 designates an original document to be scanned; 2 is a pressing platen formed of silicone rubber for pressing the original document against a glass plate 3; 4 is an original read surface; 5 is an LED element light source containing a plurality of LEDs arranged in a line; 6 is a rod lens array containing a plurality of lenses arranged in a line; 7 is an IC sensor element array; 8 is a ceramic print wiring substrate applied with a thick film printing; 9 denotes a flexible substrate for connecting the substrate 8 to the pins 10a of a connector 10; 11 denotes a frame made of aluminum with the aforementioned parts assembled thereon at predetermined positions; and 16 is a mold material or a glass cover for protecting the IC sensor element 7.
Next, the operation will be described. The original document 1 is transported in a direction as indicated by the arrow while being pressed against the original read surface 4 of the glass plate 3 upon rotation of the pressing platen 2. Original characters or the like of the original document on the read surface 4 are illuminated by the light source 5 and are focussed on the IC sensor element 7 through the rod lens array 6. Information read by the IC sensor element 7 is fed to the connector 10 through a conductor pattern (not shown) formed on the print wiring substrate 8 and the flexible print substrate 9.
The original read surface 4 is formed on the surface of the glass plate 3 fitted within the frame 11 so as not to obscure the optical system of the rod lens array 6. An internal space constituted by the frame 11 and the glass plate 3 is so sensitive to dust that when dust enters the space, read information becomes distorted, producing extra lines or gaps in information. Therefore, the aforesaid space is closed in order to prevent entry of dust from the exterior.
The conventional contact type image sensor is constructed as described above. While the sensor is protected from external dust, there are many internal parts provided. The internal construction is complicated, and the sensor is susceptible to particles such as fragments produced from the assembly of the internal parts or chips from the frame produced as a consequence of construction. Furthermore, optically, the distance between the light source 5 and the original read surface 4 is short. Therefore, there poses a problem in that irregularities in brightness between LED elements disposed in a linear array as a light source 5 are apparent on the read surface 4, thus deteriorating the image quality of the original document 1.